1. Field of the Invention
The present invention relates to a magnetic head for use to write data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head including a main pole and a write shield.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system in which the magnetization of signals is directed along the plane of a recording medium (the longitudinal direction), and a perpendicular magnetic recording system in which the magnetization of signals is directed perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure in which a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head unit includes a main pole. The main pole has an end face located in a medium facing surface facing a recording medium, and produces, from the end face, a write magnetic field in a direction perpendicular to the plane of the recording medium.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). An airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium causes the slider to slightly fly over the surface of the recording medium.
Here, the side of the positions closer to the leading end relative to a reference position will be referred to as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be referred to as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs depending on the position of the magnetic head across the tracks.
Particularly, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing. In the present application, this phenomenon will be called unwanted erasure. The unwanted erasure includes adjacent track erasure (ATE) and wide-area track erasure (WATE). To achieve higher recording densities, it is necessary to prevent the occurrence of unwanted erasure.
A known technique for preventing unwanted erasure induced by a skew is to provide a wrap-around shield and a gap section, as disclosed in U.S. Pat. No. 8,587,899 B1, for example. The wrap-around shield is a write shield having an end face that is located in the medium facing surface and surrounds the end face of the main pole. The gap section separates the wrap-around shield from the main pole.
The wrap-around shield includes a leading shield, first and second side shields, and a trailing shield. The leading shield has an end face located in the medium facing surface at a position on the leading side of the end face of the main pole. The first and second side shields have two end faces located in the medium facing surface at positions on opposite sides of the end face of the main pole in the track width direction. The trailing shield has an end face located in the medium facing surface at a position on the trailing side of the end face of the main pole.
The gap section includes a leading gap section for separating the leading shield from the main pole, first and second side gap sections for separating the first and second side shields from the main pole, and a trailing gap section for separating the trailing shield from the main pole.
The wrap-around shield has the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium, and thereby preventing the magnetic flux from reaching the recording medium. A magnetic head provided with the wrap-around shield is able to prevent unwanted erasure and provide further enhanced recording density.
The position of an end of a record bit to be recorded on the recording medium is determined by the position of the trailing-side edge (hereinafter referred to as the top edge) of the end face of the main pole in the medium facing surface. Accordingly, what are important for improving the write characteristics of the write head unit include: high write magnetic field strength at the top edge or in the vicinity thereof; and a large gradient of change in the write magnetic field strength at the top edge or in the vicinity thereof in the distribution of the write magnetic field strength in the direction in which the tracks extend.
A magnetic head provided with a wrap-around shield suffers from the problem that when a large amount of magnetic flux leaks from the main pole to the wrap-around shield, particularly to the leading shield and the first and second side shields, there occurs reductions in the write magnetic field strength and the aforementioned gradient of change at the top edge of the end face of the main pole or in the vicinity of the top edge, and the write characteristics are thereby degraded.
Now, we will discuss a configuration in which the thickness of the leading gap section is constant regardless of distance from the medium facing surface. First, assume that the thickness of the leading gap section is small. In this case, the distance between the end face of the main pole and the end face of the leading shield in the medium facing surface is small. Thus, the write shield can fully perform the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium. However, because of the small distance between the main pole and the leading shield, flux leakage from the main pole to the leading shield increases to degrade the write characteristics.
Next, assume that the thickness of the leading gap section is large. In this case, it is possible to reduce flux leakage from the main pole to the leading shield. However, since the distance between the end face of the main pole and the end face of the leading shield in the medium facing surface is large, the write shield cannot perform its function satisfactorily.
U.S. Pat. No. 8,587,899 B1 discloses a magnetic head in which the leading shield includes a base part, and a protruding part protruding from the base part toward the main pole. The protruding part has an inclined surface facing the main pole, and a rear end face opposite to the medium facing surface. The rear end face forms a greater angle with respect to a direction perpendicular to the medium facing surface than does the inclined surface. The distance between the inclined surface and the main pole is constant regardless of distance from the medium facing surface. On the other hand, the distance between the rear end face and the main pole increases with increasing distance from the medium facing surface.
The magnetic head disclosed in U.S. Pat. No. 8,587,899 B1 reduces flux leakage from the main pole to the leading shield at a location apart from the medium facing surface. In this magnetic head, however, the leading shield is small in volume and thus susceptible to flux saturations. This results in the problem that magnetic flux leaks from the the end face of the leading shield located in the medium facing surface to induce unwanted erasure.
Thus, for the magnetic head including the main pole and the write shield, it has conventionally been difficult to improve the write characteristics without compromising the function of the write shield.